Cast-in film cooling hole structures

ABSTRACT

A core element of an investment core for use in a casting process used to produce an airfoil includes an investment core body, an extension connected to and protruding from the investment core body, and a connection portion connected to the investment core body and to the extension. The investment core body comprises a ceramic material. A shape of the extension comprises a tube with a centerline axis passing through a center of the extension. A shape of a cross-section of the extension taken along a plane perpendicular to the extension centerline axis comprises an ellipse. The extension is connected to the investment core body by the connection portion.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a divisional of U.S. application Ser. No. 16/131,695filed Sep. 14, 2018 for “CAST-IN FILM COOLING HOLE STRUCTURES” by J.Paulus, D. Davis, and J. Wagner.

BACKGROUND

The present disclosure generally relates to investment casting. Inparticular, the present disclosure relates to cast-in film cooling holestructures for gas turbine engines.

Gas turbine engines are widely used in aircraft propulsion, electricpower generation, and ship propulsion. In all gas turbine engineapplications, efficiency is a prime objective. Improved gas turbineengine efficiency can be obtained by operating at higher temperatures,however current operating temperatures are at such a level that, in theturbine section, the superalloy materials used have limited mechanicalproperties. Consequently, it is a general practice to provide aircooling for components in the hottest portions of gas turbine engines,typically in the turbine section. Cooling is provided by flowingrelatively cool air from the compressor section of the engine throughpassages in the turbine components to be cooled.

Investment casting is a commonly used technique for forming metalliccomponents having complex geometries, especially hollow components, andis used in the fabrication of superalloy gas turbine engine components.Existing casting cores are fabricated from ceramic materials. Such coresare fragile, especially the advanced cores used to fabricate smallintricate cooling passages in advanced hardware. Existing cores involvelong, thin rods for simulating a machined cylindrical hole. These rodsare fragile and are prone to warpage and breaking during fabrication andmetal casting.

SUMMARY

A core element of an investment core for use in a casting process usedto produce an airfoil includes an investment core body, an extensionconnected to and protruding from the investment core body, and aconnection portion connected to the investment core body and to theextension. The investment core body comprises a ceramic material. Ashape of the extension comprises a tube with a centerline axis passingthrough a center of the extension. A shape of a cross-section of theextension taken along a plane perpendicular to the extension centerlineaxis comprises an ellipse. The extension is connected to the investmentcore body by the connection portion.

An airfoil includes a body, an airfoil wall, a cooling circuit, and acooling hole. The airfoil wall forms an exterior surface of the body.The cooling circuit is disposed within the body. The cooling hole isdisposed in a portion of the body. The cooling hole fluidly connects thecooling circuit to the exterior surface of the airfoil wall. The coolinghole includes a cavity, an outlet, and a rod of solid material. Thecavity is disposed in a portion of the airfoil wall. The cavity includesa tubular shape with a centerline axis passing through a center of thecavity. A cross-section shape of the cavity taken along a planeperpendicular to the cavity centerline comprises an ellipse. The outletfluidly connects the cavity to the exterior surface of the body and isdisposed in a portion of the exterior surface of the airfoil wall. Therod of solid material is disposed in the cavity and passes through aportion of the cavity.

A core assembly for use with an investment casting process includes acore element and a wax pattern. The core element includes a body, anextension connected to and protruding from the body, a channel disposedthrough the extension, and a connection portion connected to the bodyand to the extension. The extension is connected to the body by theconnection portion. A shape of the extension includes a tube with acenterline axis passing through a center of the extension. A shape of across-section of the extension taken along a plane perpendicular to theextension centerline axis includes an ellipse. The channel includes acenterline axis passing through a center of the channel. A shape of across-section of the channel taken along a plane perpendicular to thechannel centerline axis includes an ellipse.

A method of cooling an airfoil includes providing cooling air into acavity of a cooling hole disposed in the airfoil. The airfoil includes abody, an airfoil wall forming an exterior surface of the body, a coolingcircuit disposed within the body, and the cooling hole. The cooling holeis disposed in a portion of the body and fluidly connects the coolingcircuit to the exterior surface of the airfoil wall. The cooling holeincludes the cavity, an outlet, and a rod of solid material. The cavityis disposed in a portion of the airfoil wall. The cavity includes atubular shape with a centerline axis passing through a center of thecavity. A cross-section shape of the cavity taken along a planeperpendicular to the cavity centerline includes an ellipse. The outletfluidly connects the cavity to the exterior surface of the body and isdisposed in a portion of the exterior surface of the airfoil wall. Therod of solid material is disposed in the cavity and passes through aportion of the cavity.

A method of making an airfoil includes forming a core assembly andcreating an airfoil with the core assembly through investment casting.The core assembly includes a core element and a wax pattern. The coreelement includes a body, an extension connected to and protruding fromthe body, a channel disposed through the extension, and a connectionportion connected to the body and to the extension. The extension isconnected to the body by the connection portion. A shape of theextension includes a tube with a centerline axis passing through acenter of the extension. A shape of a cross-section of the extensiontaken along a plane perpendicular to the extension centerline axisincludes an ellipse. The channel includes a centerline axis passingthrough a center of the channel. A shape of a cross-section of thechannel taken along a plane perpendicular to the channel centerline axisincludes an ellipse. The airfoil includes a body, an airfoil wall, acooling circuit, and a cooling hole. The airfoil wall forms an exteriorsurface of the body. The cooling circuit is disposed within the body.The cooling hole is disposed in a portion of the body. The cooling holefluidly connects the cooling circuit to the exterior surface of theairfoil wall. The cooling hole includes a cavity, an outlet, and a rodof solid material. The cavity is disposed in a portion of the airfoilwall. The cavity includes a tubular shape with a centerline axis passingthrough a center of the cavity. A cross-section shape of the cavitytaken along a plane perpendicular to the cavity centerline comprises anellipse. The outlet fluidly connects the cavity to the exterior surfaceof the body and is disposed in a portion of the exterior surface of theairfoil wall. The rod of solid material is disposed in the cavity andpasses through a portion of the cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a small portion of a core element withfour extensions.

FIG. 2A is a side, cross-section view of a first core element and afirst wax pattern taken along 2-2 shown in FIG. 1.

FIG. 2B is a side, cross-section view of a second core element and asecond wax pattern.

FIG. 2C is a side, cross-section view of a third core element and athird wax pattern.

FIG. 3A is a perspective view of an airfoil with cooling holes.

FIG. 3B is another perspective view of the airfoil with another coolinghole.

FIG. 4A is a side, cross-section view of a first airfoil with a firstcooling hole.

FIG. 4B is a side, cross-section view of a second airfoil with a secondcooling hole.

FIG. 4C is a side, cross-section view of a third airfoil with a thirdcooling hole.

FIG. 4D is a side, cross-section view of a fourth airfoil with a fourthcooling hole.

FIG. 4E is a side, cross-section view of a fifth airfoil with a fifthcooling hole.

FIG. 5 is a top view taken from 5-5 shown in FIG. 4A of a portion of anexterior surface of the airfoil with two cooling hole outlets.

DETAILED DESCRIPTION

Existing ceramic cores can be produced by a molding process using aceramic slurry and a shaped die; both injection molding andtransfer-molding techniques may be employed. The pattern material ismost commonly wax although plastics, low melting-point metals, andorganic compounds such as urea, have also been employed. The shell moldis formed using a colloidal silica binder to bind together ceramicparticles which may be alumina, silica, zirconia, and alumina silicates.

The investment casting process to produce a turbine blade, using aceramic core, will be explained briefly here (although it is notdepicted in any of the figures). A ceramic core having the geometrydesired for the internal cooling passages is placed in a metal die whosewalls surround but are generally spaced away from the core. The die isfilled with a disposable pattern material such as wax. The die isremoved leaving the ceramic core embedded in a wax pattern. The outershell mold is then formed about the wax pattern by dipping the patternin a ceramic slurry and then applying larger, dry ceramic particles tothe slurry. This process is termed stuccoing. The stuccoed wax pattern,containing the core, is then dried and the stuccoing process repeated toprovide the desired shell mold wall thickness. At this point the mold isthoroughly dried and heated to an elevated temperature to remove the waxmaterial and strengthen the ceramic material.

The result is a ceramic mold containing a ceramic core which incombination define a mold cavity. It will be understood that theexterior of the core defines the passageway to be formed in the castingand the interior of the shell mold defines the external dimensions ofthe superalloy casting to be made. The core and shell may also definecasting portions such as gates and risers which are necessary for thecasting process but are not a part of the finished cast component. Afterthe removal of the wax and thermally sintering the refractory ceramicshell mold, molten superalloy material is poured into the cavity definedby the shell mold and core assembly and solidified. The mold and coreare then removed from the superalloy casting by a combination ofmechanical and chemical means.

A cast-in circular cooling hole will provide greater stability as a corefeature and allow the possibility of cooling tuning performance withoutmaking the structure excessively fragile. Structures such as a wheelwith a hole, elongations, or other features, along with variances inorientation and placement of the cast circular structure, can be used todirect and tune air flow and are disclosed herein.

FIG. 1 is a perspective view of a portion of core element 10 and showsbody 12, connection portions 14, extensions 16, centerline axis C_(LE)of extension 16, and channels 18.

Core element 10 is a small sub-portion of a larger investment core foruse in a casting process used to produce an airfoil. Core element 10 caninclude ceramic and/or refractory metal materials. For example, amaterial of core element 10 can include silica, alumina, zirconia,chromia, mullite, and hafnia, or other suitable ceramic materials, aswell as molybdenum, tantalum, niobium, tungsten, and alloys thereof.Refractory metal alloys and intermetallics such as molybdenum alloys,tungsten alloys, tantalum alloys, niobium alloys, and molybdenumdisilicide (MoSi₂), respectively, which form protective silicon dioxide(SiO₂) layers can also be employed.

Body 12 is a major portion of core element 10 that includes a generallyflat, planar shape. Connection portions 14 are intermediary sections ofcore element 10 positioned between body 12 and extensions 16. Extensions16 are tubes of casting core material. Extensions 16 can include across-section shape of an ellipse, and in this non-limiting example acircle. There can be more or less than the four extensions 16 shown inthe embodiment. Channels 18 are cylindrically shaped passages oropenings. Centerline axis C_(LE) of extension 16 is an imaginary majoraxis extending through a center of extension 16 as shown in FIG. 1.

Body 12 is connected to and formed as a single piece of material withconnection portions 14 and with extension 16. Connection portions 14 arepositioned between and connected to body 12 and extensions 16.Extensions 16 are connected to and formed with connection portions 14.Channels 18 are formed in and pass through a center of each ofextensions 16.

Core element 10 is configured as an investment core for use in a castingprocess used to produce an airfoil. The casting process can be aninvestment casting or lost wax casting process. Body 12, connectionportions 14, and extensions 16 are used as molds in the casting processto form voids or cavities in the final cast part. Channels 18 provide avoid in which a piece of wax is positioned. During the casting process,the piece of wax positioned in channels 18 is melted away allowing thecasting metal to fill and form into the void left by the wax that was inchannels 18. In this way, channels 18 represent a solid cylinder of castmaterial of the final part.

Configurations of existing cooling hole casting cores include long thinrods to simulate machined cylindrical holes. However, these rods arefragile and prone to breaking during fabrication and metal casting. Incontrast, extensions 16 of body 10 provide greater stability as a corefeature to prevent breakage of core element 10 during setup andexecution of the casting process.

FIG. 2A is a side, cross-section view taken along 2-2 shown in FIG. 1 ofcore assembly 22A that shows core element 10A (with body 12A, connectionportion 14A, extension 16A, centerline axis C_(LE) of extension 16A,channel 18A, and centerline axis C_(LC) of channel 18A) and wax pattern24A (with first wax piece 26A, second wax piece 28A, and slip area 30A).FIG. 2A also shows height H_(E) of extension 16A, width W_(E) ofextension 16A, and width W_(CP) of connection portion 14A.

As can be seen in FIG. 2A, a cross-section shape of extension 16A caninclude an ellipse, and in this non-limiting example a circle. Asprovided here, the cross-section shape of extension 16A is taken along aplane that is perpendicular to centerline axis C_(LE) of extension 16A.Height H_(E) is a height of extension 16A measured between a major faceof body 12A that is connected to connection portion 14A and an end ofextension 16A that is on an opposite or distal end of extension 16A fromconnection portion 14A. Width W_(E) is a width of extension 16A that ismeasured in a direction perpendicular to the measurement of height H_(E)of extension 16A. Width W_(CP) is a width of connection portion 14A thatis measured perpendicular to the centerline axis passing through thecenter of extension 16A.

As can be seen in FIG. 2A, a cross-section shape of channel 18A caninclude an ellipse, and in this non-limiting example a circle. Asprovided here, the cross-section shape of channel 18A is taken along aplane that is perpendicular to centerline axis C_(LC) of channel 18A.Centerline axis C_(LC) of channel 18A is an imaginary major axisextending through a center of channel 18A. In this view, centerline axisC_(LC) extends directly into and out of the page. Also with this view,centerline axis C_(LE) of extension 16A extends directly into and out ofthe page. Wax pattern 24A is an assembly of pieces of wax comprisingfirst and second wax pieces 26A and 28A in this embodiment. First waxpiece 26A and second wax piece 28A are soluble wax core pieces. Sliparea 30A is a portion of extension 16A that represents a portion of thefinal part that will be machined away (e.g., removed) from the finalpart.

In this non-limiting embodiment, centerline axis C_(LC) of channel 18Ais coaxial and parallel with centerline axis C_(LE) of extension 16A. Asshown in FIG. 2A, width W_(CP) of connection portion 14A is greater thanhalf of height H_(E) of extension 16A. Also in this embodiment, widthW_(E) of extension 16A is equal to or greater than height H_(E) ofextension 16A. First wax piece 26A is disposed in channel 18A. Secondwax piece 28A is disposed external to extension 16A and in contact withboth extension 16A and body 12A. Slip area 30A is disposed on a distalend of extension 16A away from body 12A. In the view shown in FIG. 2A,slip area 30A is positioned at a top portion of extension 16A.

Wax pattern 24A, with first wax piece 26A and second wax piece 28A, isused during the casting process by melting to create the voids in whichthe metal cast material is poured into. As such, wax pattern 24A isrepresentative of the formed portions of the final cast part. Slip area30A represents a portion of extension 16A that is to be machined awayduring the casting process. In this way, slip area 30A creates anopening in the formed final part (e.g., in the surface of the airfoil).

As mentioned above, the circular shape of extension 16A of body 10provides greater stability as a core feature to prevent breakage of coreelement 10A during setup and execution of the casting process. Here,with width W_(CP) of connection portion 14A being greater than half ofheight H_(E) of extension 16A, extension 16A and connection portion 14Aprovides a very strong and durable attachment to body 12A such thatextension 16A is not easily broken or damaged during preparation for orduring the casting process.

FIG. 2B is a side, cross-section view of core assembly 22B that showscore element 10B (with body 12B, connection portion 14B, extension 16B,centerline axis C_(LE) of extension 16B, channel 18B, and centerlineaxis C_(LC) of channel 18B) and wax pattern 24B (with first wax piece26B, second wax piece 28B, and slip area 30B).

As shown in FIG. 2B, centerline axis C_(LC) of channel 18B ishorizontally offset from centerline axis C_(LE) of extension 16B. Inother non-limiting embodiments, centerline axis C_(LC) of channel 18Bcan be vertically, or a combination of horizontally and vertically,offset from centerline axis C_(LE) of extension 16B. As will bediscussed with respect to FIG. 4B, the offset positioning of channel 18Bas shown in FIG. 2B provides an alternate discharge pattern and rate ofdischarge of a cooling fluid that is discharged from the cooling holecreated by extension 16B.

FIG. 2C is a side, cross-section view of core assembly 22C that showscore element 10C (with body 12C, connection portion 14C, extension 16C,centerline axis C_(LE) of extension 16C, channel 18C, and centerlineaxis C_(LC) of channel 18C) and wax pattern 24C (with first wax piece26C, second wax piece 28C, and slip area 30C). Second wax piece 28C isshown to include upstream portion 28C_(U) and downstream portion 28C_(D)of second wax piece 28C. As shown in FIG. 2C, the left side of thefigure represents an upstream direction and the right side represents adownstream direction, with the upstream/downstream terms relating to theeventual in-use directions of the final cast part (e.g., airfoil).

Here, an upper surface of upstream portion 28C_(U) of second wax piece28C is shown as being at a different, higher level than an upper face ofdownstream portion 28C_(D) of second wax piece 28C. The heightdifference between upstream portion 28C_(U) and downstream portion28C_(D) of second wax piece 28C allows for variations in fluid flowdischarge from a cooling hole that is to be formed from extension 16C inthe final cast part (see e.g., FIG. 4C and related discussion). Byvarying the difference in height between upstream portion 28C_(U) anddownstream portion 28C_(D) of second wax piece 28C, the flow of coolingair can be directed and tuned as needed due to operational parameters.

FIG. 3A is a perspective view of airfoil 32 and shows body 34, exteriorsurface 36, leading edge 38, trailing edge 40, suction side 42, coolingholes 46, outlets 48, tip 50, platform 52, and root 54. FIG. 3B isanother perspective view of airfoil 32 showing body 34, exterior surface36, leading edge 38, trailing edge 40, pressure side 44, cooling hole46, outlet 48, tip 50, platform 52, and root 54.

Airfoil 32 is a stator or rotor vane or blade for use in a jet turbineengine. Body 34 is a main portion of airfoil 32. Exterior surface 36 isan outside part or outermost layer of body 34. Leading edge 38 is anedge of airfoil 32 that is pointed in a generally upstream directionduring use of airfoil 32. Trailing edge 40 is an edge of airfoil 32 thatis pointed in a generally downstream direction during use of airfoil 32.Suction side 42 is a curved side of airfoil 32 that is positionedopposite from pressure side 44. Pressure side 44 is a curved side ofairfoil 32 that is positioned opposite from suction side 42. Coolingholes 46 are slots or holes disposed in exterior surface 36 of airfoil32. In the non-limiting embodiments presented in FIGS. 3A and 3B,airfoil 32 includes three cooling holes 46. Outlets 48 are openings orholes. Tip 50 is a distal end of airfoil 32. Platform 52 is a generallyplanar piece of solid material. Root 54 is a bottom base portion ofairfoil 32.

Airfoil 32 connects to a ring or a hub (not shown) of a jet turbineengine via the bottom root portion of airfoil 32. Body 34 includesleading edge 38, suction side 42, and pressure side 44. Exterior surface36 is disposed around an exterior of body 34. Leading edge 38 connectsto and extends between suction side 42 and pressure side 44. Trailingedge 40 connects to and extends between suction side 42 and pressureside 44 on an opposite end of body 34 from leading edge 38. Suction side42 wraps around a side of airfoil 32 and connects to leading edge 38 atan upstream portion of airfoil 32 and to pressure side 44 at adownstream portion of leading edge 32. Pressure side 44 wraps around anopposite side of airfoil 32 and connects to leading edge 38 at anupstream portion of airfoil 32 and to suction side 42 at a downstreamportion of leading edge 32. Cooling holes 46 are disposed in body 34 andcreate a fluidic passage through exterior surface 36. As will bediscussed with respect to FIGS. 4A-4C, cooling holes 46 are fluidlyconnected to a cooling circuit positioned inside of body 34. Outlets 48are disposed in exterior surface 36 and are fluidly connected to coolingholes 46. Tip 50 is connected to a distal end of body 34 of airfoil 32.Platform 52 is disposed between body 34 and root 54. Root 54 isconnected to platform 52.

Airfoil 32 creates an aerodynamic force resulting from air passing overairfoil 32. Body 34 connects leading edge 38, suction side 42, andpressure side 44 together. Exterior surface 36 provides a solid barrierof body 34 that deflects air from exterior surface 36 during use ofairfoil 32. During use of airfoil 32, leading edge 38 comes into contactwith and redirects air around suction and pressure sides 40A and 40B ofairfoil 32. The convex and concave contours of suction side 42 andpressure side 44 create a pressure gradient between the air flowingacross suction and pressure sides 40A and 40B. Cooling holes 46 delivercooling air from body 34 to exterior surface 36 such that the coolingair absorbs thermal energy from body 34 as the cooling air flows acrossexterior surface 36 of airfoil 32.

FIG. 4A is a side, cross-section view of airfoil 32A and shows body 34A,exterior surface 36A, cooling hole 46A, wall 58A, cooling circuit 60A,cavity 56A, centerline axis C_(LC) of cavity 56A, outlet 48A, rod 62A,centerline axis C_(LR) of rod 62A, inlet 64A, first cusp 66A, secondcusp 68A, first sidewall 70A, and second sidewall 72A.

Cooling hole 46A of FIG. 4A has been formed by core element 10A of FIG.2A by investment casting in which metal replaces wax, and subsequentlythe ceramic is removed to form cooling hole 46A and cooling circuit 60A.Cooling hole 46A corresponds to extension 16A shown in FIG. 2A andincludes cavity 56A, outlet 48A, and rod 62A. Airfoil 32A can includemore than one cooling hole 46A. Wall 58A corresponds to second wax piece28A shown in FIG. 2A and includes a generally flat, planar piece ofsolid material. Cooling circuit 60A corresponds to body 12A shown inFIG. 2A and includes an assembly of fluidic channels and cavities.Cavity 56A corresponds to extension 16A shown in FIG. 2A and includes achamber. As shown in FIG. 2A, a cross-section shape of cavity 56Agenerally includes an ellipse, and in particular a circle. A shape ofcavity 56A generally includes a tube.

Centerline axis C_(LC) is an imaginary major axis extending through acenter of cavity 56A. In this view, centerline axis C_(LC) extendsdirectly into and out of the page. Outlet 48A corresponds to aninterface between extension 16A and slip area 30A shown in FIG. 2A andincludes an opening or hole. Rod 62A corresponds to channel 18A shown inFIG. 2A and includes a cylindrically shaped piece of solid material. Asshown in FIG. 2A, a cross-section shape of rod 62A generally includes anellipse, and in particular a circle. Centerline axis C_(LR) is animaginary major axis extending through a center of rod 62A. In thisview, centerline axis C_(LR) of rod 62A extends directly into and out ofthe page.

Inlet 64A is a fluidic opening extending between first cusp 66A andsecond cusp 68A. First cusp 66A and second cusp 68A are curved corners.First cusp 66A is formed at a location where first sidewall 70A meetscooling circuit 60A. Second cusp 68A is formed at a location wheresecond sidewall 72A meets cooling circuit 60A. First sidewall 70A andsecond sidewall 72A are arcuate or curved sidewalls of cavity 56A.Cooling hole 46A is disposed in a portion of exterior surface 36A and isfluidly connected to cooling circuit 60A. Cooling hole 46A can bedisposed on or in any of leading edge 38, suction side 42, and/orpressure side 44 of airfoil 32 (as shown in FIGS. 3A and 3B). Wall 58Ais positioned on both sides of cooling hole 46A and extends betweenexterior surface 36A and cooling circuit 60A. Cooling circuit 60A isdisposed in an interior portion of airfoil 32A and is fluidly connectedto cavity 56A. Cavity 56A is disposed in body 34A and is fluidlyconnected to cooling circuit 60A and to outlet 48A. In this non-limitingembodiment, centerline axis C_(LC) of cavity 56A is parallel to andcoaxial with centerline axis C_(LR) of rod 62A. Outlet 48A is disposedin a portion of exterior surface 36A of wall 58A. Outlet 48A fluidlyconnects cavity 56A to exterior surface 36A of body 34A. Rod 62A isdisposed in and passes through a portion of cavity 56A.

Inlet 64A extends between first cusp 66A and second cusp 68A and forms afluidic connection point between cooling circuit 60A and cavity 56A.First cusp 66A is located on an upstream (to the left in FIG. 4A) end ofinlet 64A and second cusp is located on a downstream (to the right inFIG. 4A) side of inlet 64A. The curvatures of first sidewall 70A andsecond sidewall 72A create a bulbous, generally circular shape of cavity56A.

An investment casting process to produce or form airfoil 32A, using coreelement 10A, can be the following. Core element 10A, having the geometrydesired for cooling circuit 60A, is placed in a metal die whose wallssurround but are generally spaced away from core element 10A. The die isfilled with a disposable pattern material such as wax pattern 24A. Thedie is removed leaving core element 10A embedded in wax pattern 24A. Theouter shell mold is then formed about wax pattern 24A by dipping waxpattern 24A in a ceramic slurry and then applying larger, dry ceramicparticles to the slurry. This process is termed stuccoing. The stuccoedwax pattern 24A, containing core element 10A, is then dried and thestuccoing process repeated to provide the desired shell mold wallthickness. At this point the mold is thoroughly dried and heated to anelevated temperature to remove wax pattern 24A and strengthen theceramic material of core element 10A.

The result is a ceramic mold containing core element 10A which incombination define a mold cavity. It will be understood that theexterior of core element 10A defines the passageway to be formed in thecasting and the interior of the shell mold defines the externaldimensions of the casting, or airfoil 32 to be made. Core element 10Aand shell may also define casting portions such as gates and riserswhich are necessary for the casting process but are not a part of thefinished cast component. After the removal of wax pattern 24A andthermally sintering the refractory ceramic shell mold, molten material(e.g., superalloy) is poured into the cavity defined by the shell moldand core element 10A and is solidified. The mold and core element 10Aare then removed from the casting by a combination of mechanical andchemical means.

In following this casting process, first wax piece 26A is removed duringthe casting process and is replaced by wall 58A of airfoil 32 whilesecond wax piece 28A is removed and replaced with rod 62A. Also duringthe casting process, body 12A is removed and replaced with coolingcircuit 60A and extension 16A is removed and replaced with cavity 56A.Similar removing and replacing occurs with respect to the embodimentsshown and is discussed with respect to FIGS. 2B and 4B, as well as FIGS.2C and 4C.

Cooling circuit 60A provides and delivers a source of cooling air tocooling hole 46A. Cooling air travels through cooling circuit 60A, isdelivered to cavity 56A through inlet 64A, travels around both sides ofrod 62A along first sidewall 70A and second sidewall 72A, is pushed outof outlet 48A, and is then delivered to exterior surface 36A of airfoil32A. In this example, with centerline axis C_(LC) of cavity 56A beingcoaxial with centerline axis C_(LR) of rod 62A, a flow of cooling airthat flows around rod 62A is evenly distributed around the two sides ofrod 62A and provides a first cooling air flow distribution pattern outof outlet 48A and along exterior surface 36A.

The configuration of airfoil 32A with cooling hole 46A is fundamentallydifferent from existing configurations of a machined hole in that thecooling air can approach outlet 48A from two directions (e.g., aroundboth sides of rod 62A) instead of from just a single direction. In anexample with airfoil 32A spinning, the spinning energy of airfoil 32Awill direct the cooling air to exit cooling hole 46A in an intendeddirection. The configuration of cooling hole 46A is also useful onleading edge 38 of airfoil 32A, such as where “showerheads” of filmcooling holes are currently used in existing designs, due to thevariations and tuning of how the cooling air is directed out of coolinghole 46A. The configuration shown in FIG. 4A (and in FIGS. 4B and 4C)additionally limits back-flow of the cooling air in the opposingdirection rather than choking in a narrow opening such as can occur inexisting single-passage drilled cooling hole designs.

FIG. 4B is a side, cross-section view of airfoil 32B and shows body 34B,exterior surface 36B, cooling hole 46B, wall 58B, cooling circuit 60B,cavity 56B, centerline axis C_(LC) of cavity 56B, outlet 48B, rod 62B,and centerline axis C_(LR) of rod 62B.

Cooling hole 46B of FIG. 4B has been formed by core element 10B of FIG.2B by investment casting in which metal replaces wax, and subsequentlythe ceramic is removed to form cooling hole 46B and cooling circuit 60B.In this embodiment, cooling hole 46B corresponds to extension 16B, wall58B corresponds to second wax piece 28B, cooling circuit 60B correspondsto body 12B, cavity 56B corresponds to extension 16B, outlet 48Bcorresponds to an interface between extension 16B and slip area 30B, androd 62B corresponds to channel 18B each of which are shown in FIG. 2B.As shown in FIG. 4B, centerline axis C_(LR) of rod 62B is offset fromcenterline axis C_(LC) of cavity 56B. Additionally, centerline axisC_(LR) of rod 62B is parallel to centerline axis C_(LC) of cavity 56B.In this non-limiting embodiment, centerline axis C_(LR) of rod 62B ishorizontally offset from centerline axis C_(LC) of cavity 56B. In othernon-limiting embodiments, centerline axis C_(LR) of rod 62B can bevertically, or a combination of horizontally and vertically, offset fromcenterline axis C_(LC) of cavity 56B.

With centerline axis C_(LR) of rod 62B being offset from centerline axisC_(LC) of cavity 56B, the flow of cooling air that flows around rod 62Bcan be unevenly distributed around the two sides of rod 62B to provide asecond cooling air flow distribution pattern out of outlet 48B and alongexterior surface 36B. Depending on the operational parameters, theamount of flow on both sides of rod 62B can be controlled and tuned byplacement of rod 62B to control the net flow of cooling air and thesecond cooling air flow distribution pattern out of outlet 48B. Forexample, an offset centerline axis C_(LR) of rod 62B can be used in asituation where airfoil 32B is not spinning or is static (e.g., in theinstance of airfoil 32B being a stator blade or vane).

FIG. 4C is a side, cross-section view of airfoil 32C and shows body 34C,exterior surface 36C, cooling hole 46C, wall 58C (with upstreamthickness T_(UP) and downstream thickness T_(DOWN)), cooling circuit60C, cavity 56C, centerline axis C_(LC) of cavity 56C, outlet 48C, rod62C, and centerline axis C_(LR) of rod 62C.

Cooling hole 46C of FIG. 4C has been formed by core element 10C of FIG.2C by investment casting in which metal replaces wax, and subsequentlythe ceramic is removed to form cooling hole 46C and cooling circuit 60C.In this embodiment, cooling hole 46C corresponds to extension 16B, wall58C corresponds to second wax piece 28C, cooling circuit 60C correspondsto body 12C, cavity 56C corresponds to extension 16C, outlet 48Ccorresponds to an interface between extension 16C and slip area 30C, androd 62C corresponds to channel 18C each of which are shown in FIG. 2C.Upstream thickness T_(UP) is a thickness of a portion of wall 58Clocated upstream (to the left in FIG. 4C) of outlet 48C, as measuredvertically and as shown in FIG. 4C. Downstream thickness T_(DOWN) is athickness of a portion of wall 58C located downstream (to the right inFIG. 4C) of outlet 48C, as measured vertically and as shown in FIG. 4C.

As shown in FIG. 4C, exterior surface 36C undulates at a location ofcooling hole 46C in a direction from upstream of cooling hole 46C (tothe left in FIG. 4C) to downstream of cooling hole 46C (to the right inFIG. 4C) such that the thickness of wall 58C changes from upstreamthickness T_(UP) to downstream thickness T_(DOWN) at a location ofoutlet 48C. In this example, upstream thickness T_(UP) is greater thandownstream thickness T_(DOWN) relative to a downstream direction ofairflow across airfoil 32C. In other non-limiting embodiments, upstreamthickness T_(UP) can be equal to or greater than downstream thicknessT_(DOWN) in a downstream direction, or in another direction not parallelto a downstream direction. The configuration of cooling holes 46C asshown in FIG. 4C provides for further tuning and directional control ofthe flow of cooling air out of outlet 48C onto exterior surface 36C.

FIG. 4D is a side, cross-section view of airfoil 32D and shows body 34D,exterior surface 36D, cooling hole 46D, wall 58D, cooling circuit 60D,cavity 56D, centerline axis C_(LC) of cavity 56D, outlet 48D, rod 62D,and centerline axis C_(LR) of rod 62D.

In this embodiment, a cross section shape of cavity 56D taken along aplane perpendicular to centerline axis C_(LC) of cavity 56D includes anellipse. Also in this embodiment, a cross section shape of rod 62E takenalong a plane perpendicular to centerline axis C_(LR) of rod 62Dincludes an ellipse. For example, an elongated portion of rod 62Dextends in a vertical direction, with the horizontal width of rod 62Dbeing less than the vertical height of rod 62D. Likewise, an elongatedportion of cavity 56D extends in a vertical direction, with thehorizontal width of cavity 56D being less than the vertical height ofcavity 56D. In other non-limiting embodiments, the cross section shapesof cavity 56D and/or of rod 62 can include non-elliptical shapes.

Here, centerline axis C_(LC) of cavity 56D is shown as being parallel toand coaxial with centerline axis C_(LR) of rod 62D. In othernon-limiting embodiments, centerline axis C_(LR) of rod 62D can beoffset vertically and/or horizontally from centerline axis C_(LC) ofcavity 56D. The configuration of cooling hole 46D with elongated cavity56D and rod 62D allow for further variation and tuning of the flow ofcooling air through cavity 56D, out of outlet 48D, and onto exteriorsurface 36D.

FIG. 4E a side, cross-section view of airfoil 32E and shows body 34E,exterior surface 36E, cooling hole 46E, wall 58E, cooling circuit 60E,cavity 56E, centerline axis C_(LC) of cavity 56E, outlet 48E, rod 62E,and centerline axis C_(LR) of rod 62E.

Similar to the embodiment shown in FIG. 4D, a cross section shape ofcavity 56E taken along a plane perpendicular to centerline axis C_(LC)of cavity 56E includes an ellipse. Also in this embodiment, a crosssection shape of rod 62E taken along a plane perpendicular to centerlineaxis C_(LR) of rod 62E includes an ellipse. However, in comparison tocooling hole 46D shown in FIG. 4D, FIG. 4E shows an elongated portion ofrod 62E extending in a horizontal direction, with the horizontal widthof rod 62E being greater than the vertical height of rod 62E. Likewise,an elongated portion of cavity 56E extends in a horizontal direction,with the horizontal width of cavity 56E being greater than the verticalheight of cavity 56E.

The elongated configurations of cavities 48D and 48E, as well as of rods52D and 52E allow for further tuning and control of the cooling airoutput from cooling holes 46D and 42E, respectfully.

FIG. 5 is a top view taken from 5-5 shown in FIG. 4A of a portion ofexterior surface 36A of airfoil 32A with first outlet 48A, rods 62A, andsecond outlet 74. In the view shown in FIG. 5, an upstream direction isto the left of the figure and a downstream direction is to the right ofthe figure. First outlet 48A is a rectangular shaped hole or passageextending into exterior surface 36A of airfoil 32A. Second outlet 74 isa flared hole or passage extending into exterior surface 36A of airfoil32A. In this example, a shape of second outlet 74 includes an isoscelestrapezoid. In other non-limiting embodiments, the shape of second outlet74 can include other types of trapezoids such as acute, right, obtuse,parallelogram, rhombus, or square. Second outlet 74 can also include anellipse, a circle, a semi-circle, a triangle, a rhombus, a polygon, oranother geometric shape.

The variation in shape of flared second outlet 74 provides for adiffused exit pattern of cooling air from second outlet 74. Thisvariation in exit pattern can also include slowing down or speeding up avelocity of the cooling air as the cooling air exits second outlet 74 soas to adjust the cooling effects of the cooling flow as needed basedupon operational parameters.

DISCUSSION OF POSSIBLE EMBODIMENTS

The following are non-exclusive descriptions of possible embodiments ofthe present invention.

A core element includes a body, an extension connected to and protrudingfrom the body, and a connection portion connected to the body and to theextension. A shape of the extension comprises a tube with a centerlineaxis passing through a center of the extension. A shape of across-section of the extension taken along a plane perpendicular to theextension centerline axis comprises an ellipse. The extension isconnected to the body by the connection portion. The core element isconfigured as an investment core for use in a casting process used toproduce an airfoil.

The core element of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components.

The shape of the cross-section of the extension can comprise a circle.

A channel can be disposed through the extension, wherein the channel cancomprise a centerline axis passing through a center of the channel,wherein a shape of a cross-section of the channel taken along a planeperpendicular to the channel centerline axis can comprise an ellipse.

The shape of the cross-section of the channel can comprise a circle.

The centerline axis of the channel can be coaxial with the centerlineaxis of the extension.

The centerline axis of the channel can be offset from the centerlineaxis of the extension.

The centerline axis of the channel can be parallel to the centerlineaxis of the extension.

A width of the connection portion can be greater than half of a heightof the extension, wherein the width of the connection portion can bemeasured perpendicular to the centerline axis passing through the centerof the extension, and/or wherein the height of the extension can bemeasured between a major face of the body that can be connected to theconnection portion and an end of the extension that can be on anopposite end of the extension from the connection portion.

A width of the extension can be equal to or greater than the height ofthe extension, wherein the width of the extension can be measured in adirection parallel to the measurement of the extension height.

An airfoil includes a body, an airfoil wall, a cooling circuit, and acooling hole. The airfoil wall forms an exterior surface of the body.The cooling circuit is disposed within the body. The cooling holedisposed in a portion of the body. The cooling hole fluidly connects thecooling circuit to the exterior surface of the airfoil wall. The coolinghole includes a cavity, an inlet, an outlet, and a rod of solidmaterial. The cavity is disposed in a portion of the airfoil wall. Thecavity includes a tubular shape with a centerline axis passing through acenter of the cavity. A cross-section shape of the cavity taken along aplane perpendicular to the cavity centerline comprises an ellipse. Theinlet fluidly connects the cooling circuit to the cavity. The outletfluidly connects the cavity to the exterior surface of the body and isdisposed in a portion of the exterior surface of the airfoil wall. Therod of solid material is disposed in the cavity and passes through aportion of the cavity.

The airfoil of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingfeatures, configurations and/or additional components.

The exterior surface can undulate at a location of the cooling hole in adirection from upstream of the cooling hole to downstream of the coolinghole such that a thickness of the airfoil wall can change at a locationof the outlet of the cooling hole.

A shape of the outlet can include a flared portion.

The shape of the cross-section of the cavity can comprise a circle.

A centerline axis of the rod can be parallel to the centerline axis ofthe cavity.

The centerline axis of the rod can be coaxial with the centerline axisof the cavity.

A shape of a cross-section of the rod can comprise an ellipse.

A core assembly for use with an investment casting process includes acore element and a wax pattern. The core element includes a body, anextension connected to and protruding from the body, a channel disposedthrough the extension, and a connection portion connected to the bodyand to the extension. The extension is connected to the body by theconnection portion. A shape of the extension includes a tube with acenterline axis passing through a center of the extension. A shape of across-section of the extension taken along a plane perpendicular to theextension centerline axis includes an ellipse. The channel includes acenterline axis passing through a center of the channel. A shape of across-section of the channel taken along a plane perpendicular to thechannel centerline axis includes an ellipse.

The wax pattern first piece can comprise a rod of wax.

A method of making an airfoil includes forming a core assembly andcreating an airfoil with the core assembly through investment casting.The core assembly includes a core element and a wax pattern. The coreelement includes a body, an extension connected to and protruding fromthe body, a channel disposed through the extension, and a connectionportion connected to the body and to the extension. The extension isconnected to the body by the connection portion. A shape of theextension includes a tube with a centerline axis passing through acenter of the extension. A shape of a cross-section of the extensiontaken along a plane perpendicular to the extension centerline axisincludes an ellipse. The channel includes a centerline axis passingthrough a center of the channel. A shape of a cross-section of thechannel taken along a plane perpendicular to the channel centerline axisincludes an ellipse. The airfoil includes a body, an airfoil wall, acooling circuit, and a cooling hole. The airfoil wall forms an exteriorsurface of the body. The cooling circuit is disposed within the body.The cooling hole disposed in a portion of the body. The cooling holefluidly connects the cooling circuit to the exterior surface of theairfoil wall. The cooling hole includes a cavity, an outlet, and a rodof solid material. The cavity is disposed in a portion of the airfoilwall. The cavity includes a tubular shape with a centerline axis passingthrough a center of the cavity. A cross-section shape of the cavitytaken along a plane perpendicular to the cavity centerline comprises anellipse. The outlet fluidly connects the cavity to the exterior surfaceof the body and is disposed in a portion of the exterior surface of theairfoil wall. The rod of solid material is disposed in the cavity andpasses through a portion of the cavity.

The method of the preceding paragraph can optionally include,additionally and/or alternatively, any one or more of the followingsteps, features, configurations and/or additional components.

The first piece of the wax pattern can be removed from the channel ofthe core element and/or the first piece of the wax pattern can bereplaced with the rod, the second piece of the wax pattern can beremoved and/or the second piece of the wax pattern can be replaced withthe body of the airfoil, the extension of the core element can beremoved to form the cavity of the cooling hole, and/or the body of thecore element can be removed to form the airfoil cooling circuit.

While the invention has been described with reference to an exemplaryembodiment(s), it will be understood by those skilled in the art thatvarious changes may be made and equivalents may be substituted forelements thereof without departing from the scope of the invention. Inaddition, many modifications may be made to adapt a particular situationor material to the teachings of the invention without departing from theessential scope thereof. Therefore, it is intended that the inventionnot be limited to the particular embodiment(s) disclosed, but that theinvention will include all embodiments falling within the scope of theappended claims.

1. A core element of an investment core for use in a casting processused to produce an airfoil, the core element comprising: a investmentcore body comprising a ceramic material; an extension comprising aceramic material, wherein the extension is connected to and protrudingfrom the investment core body, wherein a shape of the extensioncomprises a tube with a centerline axis passing through a center of theextension, wherein a shape of a cross-section of the extension takenalong a plane perpendicular to the extension centerline axis comprisesan ellipse; and a connection portion comprising a ceramic material,wherein the connection portion is connected to the investment core bodyand to the extension, wherein the extension is connected to theinvestment core body by the connection portion.
 2. The core element ofclaim 1, wherein the shape of the cross-section of the extensioncomprises a circle.
 3. The core element of claim 1, further comprising achannel disposed through the extension, wherein the channel comprises acenterline axis passing through a center of the channel, wherein a shapeof a cross-section of the channel taken along a plane perpendicular tothe channel centerline axis comprises an ellipse.
 4. The core element ofclaim 3, wherein the shape of the cross-section of the channel comprisesa circle.
 5. The core element of claim 1, wherein the centerline axis ofthe channel is coaxial with the centerline axis of the extension.
 6. Thecore element of claim 1, wherein the centerline axis of the channel isoffset from the centerline axis of the extension.
 7. The core element ofclaim 1, wherein the centerline axis of the channel is parallel to thecenterline axis of the extension.
 8. The core element of claim 1,wherein a width of the connection portion is greater than half of aheight of the extension, wherein the width of the connection portion ismeasured perpendicular to the centerline axis passing through the centerof the extension, and wherein the height of the extension is measuredbetween a major face of the investment core body that is connected tothe connection portion and an end of the extension that is on anopposite end of the extension from the connection portion.
 9. The coreelement of claim 8, wherein a width of the extension is equal to orgreater than the height of the extension, wherein the width of theextension is measured in a direction parallel to the measurement of theextension height.
 10. A core assembly for use with an investment castingprocess, the core assembly comprising: a core element from claim 1; anda wax pattern comprising: a first piece disposed in the channel; and asecond piece disposed externally from the extension, the second piece ofthe wax pattern in contact with the extension and with the body.
 11. Thecore assembly of claim 10, wherein the wax pattern first piece comprisesa rod of wax.